
<!DOCTYPE html>
<html>

<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .horizontal-line {
            position: relative;
            margin: 75px 0;
            width: 100%;
            height: 1px;
        }

        .horizontal-line:before {
            content: "";
            position: absolute;
            background-image: linear-gradient(to left, #777, transparent);
            left: 10%;
            right: 50%;
            height: 1px;
        }

        .horizontal-line:after {
            content: "";
            position: absolute;
            background-image: linear-gradient(to right, #777, transparent);
            left: 50%;
            right: 10%;
            height: 1px;
        }
    </style>
</head>

<body>
    <div class="horizontal-line"></div>
</body>

</html>